Cinnamic Acid

Cinnamic Acid, $C\_6H\_5CH\; =\; CHCOOH$, exists in the free state in the balsams of Tolu and Peru, in liquid storax, and in gum benzoin. When oil of cinnamon (see below) is exposed to the air, it absorbs oxygen and deposits crystals of cinnamic acid. Cinnamic acid forms colourless crystals readily soluble in alcohol, ether, and boiling water, but sparingly soluble in cold water. It is not of any importance in the arts, and is chiefly interesting as being the acid corresponding to oil of cinnamon. This oil is the aldehyde of cinnamic acid, and is represented by the formula $C\_6H\_5CH\; =\; CHCOH$. Although isomeric with oil of cassia, it has a slightly different flavour, and is much more expensive. Both of these oils are employed in medicine as aromatic stimulants, but chiefly as pleasant adjuncts to disguise the taste of nauseous drugs. From a chemical point of view, the cinnamic acid and oil of cinnamon are related to Benzoic Acid (q.v.) and Oil of Bitter Almonds (q.v.). Benzoic acid is regarded as $C\_6H\_5COOH$, while the oil of bitter almonds is the corresponding aldehyde $C\_6H\_5COH$. On oxidation cinnamic acid is changed into benzoic acid.